1. Field of the Invention
This invention relates to detecting of the attachment of a peripheral device to a computing system, and more particularly, to detecting the attachment of a conventional cable connector to a port connector of the system.
2. Background Information
Personal computer systems generally include a system unit connected to a number of peripheral devices by means of cables extending from the peripheral devices to be connected to port connectors on the system unit. A number of types of connectors have been developed and standardized, with specific connector-types being used for connection to specific types of devices, such as keyboards, parallel devices such as printers, serial devices, video monitors, and devices using the SCSI (Small Computer Serial Interface) interface. These connector types generally include a number of mating contact terminals extending into engagement with one another through openings in mating conductive shields of the connectors. A shield of this type includes a flange extending around the opening, toward the opposite mating connector, so that the flanges of mating connectors move inside one another, in sliding contact, as the connectors are engaged. These mating shields typically form part of a conductive shielding arrangement surrounding the system unit, the peripheral device, and the interconnecting cable. This conductive shielding arrangement prevents the radiation, from the computer system, of certain electromagnetic signals which could otherwise result in EMI (electromagnetic interference) with communication signals.
The use of portable and mobile computing equipment has created an increasing need to change the configuration of a computing system on a frequent basis. For example, a laptop computer may be disconnected from various peripheral devices in an office, taken home for use at night, and reconnected to the office peripheral devices in the morning. Such an increased need to unplug and replug cable connectors leads to an increased probability that some cables will inadvertently be left unplugged. What is needed is a simple way of detecting whether a cable is connected, so that this information can be transferred to application programs and to the user as appropriate.
One method which has been used to detect the attachment of various types of peripheral devices is the sensing of various jumper configurations in a the connector of the peripheral device. For example, if three contact positions--A, B, and C--extending between the port connector and the device connector are used for this purpose, five combinations can be detected--no jumpers, a single jumper between contact positions A and B, a single jumper between contact positions B and C, a single jumper between contact positions A and C, and jumpers connecting A, B, and C. The condition of no jumpers also exists when no cable is plugged onto the device connector. This method is used at the connection between the video port of a personal computer and the cable to a video display device, in order to discriminate among several different types of display devices, requiring different driving signals, which may be alternately connected to the video port. However, since this method requires the use of additional contact positions in both the port connector and the connector of the cable to the device, it can only be used in applications where such contact positions have been provided.
A typical computer user has a need to use a number of existing peripheral devices when a new system unit is added. For this reason, it is particularly desirable to make a system unit having new features compatible with formerly manufactured versions of peripheral devices. Furthermore, it is undesirable to proliferate required configurational differences throughout both system units and peripheral devices. For example, any method providing for detection of the attachment of a peripheral device should function properly with existing, unmodified versions of the peripheral device. What is needed is a method, which may be applied to a system unit or other type of unit to which a peripheral device is attached, for detecting the attachment of the peripheral device, without requiring changes to the circuits of the peripheral device or to the connector of the cable extending from this peripheral device. In particular, additional contact positions in this connector should not be required to provide the attachment detection function.
3. Description of the Prior Art
A number of U.S. patents describe connector apparatus which use the closure of a switch within a first connector, attached to the device in which the feature is provided. The switch is closed by a feature within a second connector, mating with the first connector. An extra pair of wires, from the device in which the feature is provided, are attached to the opposite sides of the switch.
For example, U.S. Pat. No. 5,061,204 to Murakami describes a prior art system in which a flexible metal contact is held against a stationary contact in the first connector by a flexible insulating member extending within the second connector. Wires extend from the flexible and stationary contact to provide the electrical indication needed for this feature. If the two connectors are not engaged, the flexible metal contact is held, by its own shape, away from the stationary contact; if the two connectors are not completely engaged, the flexible insulating member is held away from the flexible metal contact by an interposing structure of the first connector.
Murikami teaches a connector arrangement having a movable part, slidably mounted to move in a longitudinal direction within the first connector. A conductive path extends along each side of the movable part in electrical contact with an adjacent electrical terminal of the connector. The first connector also includes a flexible insulating latch. As the two connectors are slid into engagement, an edge of the second conductor slides the movable part within the first connector toward a tip of the latch, while an interposing structure of the second connector deflects the latch away from the movable part. When the connectors are fully engaged, the latch clears the interposing structure, to rotate upward into engagement with the movable part. A conductive path extending along the tip of the latch forms an electrical connection between the conductive paths extending along the opposite sides of the movable part.
Additional connector arrangements of this general type are described in U.S. Pat. No. 5,131,865 to Taguchi, et al.
U.S. Pat. No. 4,915,649 to Shimazu, et al., describes a first connector having a contact piece, with a base portion and bifurcated free ends, held in place adjacent to a pair of contact terminals. One of the free ends is held in contact with one of the contact terminals, and the other of the free ends is moved into contact with the other contact terminal by an arm extending from the second connector when the two connectors are fully engaged.
A limitation of these methods arises from the fact that, in each case, a specialized feature of the second connector is required to effect the switch closure. The prior art described by Murakami requires a flexible member extending in the second connector to close the contacts. The connector system taught by Murakami requires an interposing structure of the second connector to deflect the flexible member of the first connector, along with a contact terminal arrangement providing space for the movable member and for a contact terminal on each side of the movable member for use with the detection feature. The system described by Shimazu, et al., requires an arm extending from the second connector to close the contacts. The need for such features means that this method cannot be readily used in a system requiring the detection, for example, of the attachment of cabled peripheral devices not configured in anticipation of providing for such detection, since the second connector is the one forming part of the cable assembly extending from such a peripheral device.
Another method for providing the detection feature includes provisions for an additional contact pair within the first and second connectors. In this way, an additional electrical path is provided, so that a ground, voltage condition, or other signal from a peripheral device or cable can be returned to activate the detection feature.
This method is described, for example, in U.S. Pat. No. 3,611,261 to Gregory. In this example, one of the connectors has a barbed resilient limb, while the other connector has an apertured lug. Electrical contact surfaces extend adjacent to the barb and the aperture. As the connectors are moved into engagement, these contact surfaces are moved apart by interposition of the barb. When these connectors are fully engaged, the barb extends into the aperture, with the contact surfaces held together to complete the detection circuit.
U.S. Pat. No. 3,414,806 to Carr describes a version of this method in which the pin used for detecting contact engagement is provided with a resistive portion. When the connectors are partly engaged, contact is made with the resistive portion; when the connectors are fully engaged, contact is made with a conductive portion of the pin.
Another example of this method is described by Klim, et al., in the IBM Technical Disclosure Bulletin, June, 1993, Vol. 30, No. 6, p. 371. In this example, a pluggable unit, such as a keyboard or a mouse, is plugged into a system unit by a cable having a connector. Electrical ground is carried to the pluggable unit from the system unit by conventional means, and a ground return line is added to the cable and connectors to return an electrical ground condition from the pluggable device to the system unit. Within the system unit, the contact engaging the ground return line is connected to a detection circuit and to a positive voltage through a pull-up resistor. When the pluggable unit is disconnected, the input to the detection circuit is held at the high level of the positive voltage; when the pluggable unit is connected, the input to the detection circuit is held at electrical ground.
These methods also have the disadvantage of requiring specialized features of the second connector. An additional connection terminal, together with associated wiring, is required. What is needed is a method allowing detection of the attachment of standard, widely-used connector types not having such features. Such a method is needed both to allow the detection of the attachment of conventional peripheral devices with standard connectors and to reduce the additional costs incurred through the use of specialized connectors.
U.S. Pat. No. 4,903,340 to Sorensen describes the use of a magnetically activated reed switch to detect the physical closure of an optical data link extending through a pair of connectors. Again, this method requires the presence of a specialized feature, in the form of a permanent magnet, as a part of the second connector.